1. Field of the Invention
The present invention relates to microprocessing in manufacturing process of semiconductor devices etc., and more particularly, to a multilayer resist method that enables finer patterning with a thin photoresist film by using a high energy beam such as KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), F2 laser light (157 nm), electron beam or X-ray as an exposure light source. More specifically, the present invention relates to a substrate for the multilayer resist method comprising at least an organic film, an antireflection silicone resin film over the organic film, and a photoresist film over the antireflection silicone resin film, a method for producing the substrate, and a patterning process with the substrate.
2. Description of the Related Art
As higher integration and higher speed of LSI are realized, finer pattern size is achieved rapidly. Along with the achievement of finer pattern size, the lithography techniques have accomplished micropatterning by using light sources with shorter wavelength and properly selecting photoresist film compositions corresponding to the light sources. As for such compositions, positive photoresist film compositions used as a monolayer are mainly selected. Each of these monolayer positive photoresist film compositions has a structure with etching resistance against etching with chlorine-containing-gas plasma or fluorine-containing-gas plasma in the resin of the composition, and has resist mechanism that an exposed area turns soluble. Such a photoresist film composition is applied to a substrate, and a resist pattern is formed on the photoresist film by dissolving an exposed area. Then the substrate is etched by using the photoresist film on which the resist pattern is formed as an etching mask.
However, when a pattern is rendered finer, that is, a pattern width is narrowed, without changing the thickness of a photoresist film to be used, resolution of the photoresist film is deteriorated. And developing the pattern on the photoresist film with a developer causes pattern collapse because the so-called aspect ratio of the pattern becomes too high. Therefore, the thickness of a photoresist film has been thinner along with achieving a finer pattern.
On the other hand, the use of shorter wavelength exposure radiations requires resins with low absorbance at the wavelength to be used for photoresist film compositions. Accordingly, as the radiation shifts from i-line to KrF and to ArF, the resin shifts from novolac resins to polyhydroxystyrene, and to acrylic resins. Along with this shift, an etching rate of a resin actually becomes high under the etching conditions mentioned above.
As a result, a substrate has to be etched with a thinner resist film having lower etching resistance. The need to provide a photoresist film with high etching resistance has become urgent.
On the other hand, a bilayer resist method, which is one of the so-called multilayer resist method, has been developed so far. In the bilayer resist method, a photoresist film and a lower film are used. The photoresist film on which a fine pattern can be formed has low etching resistance under etching conditions for processing a substrate. The lower film has enough etching resistance for processing a substrate, and can be patterned under conditions that the photoresist film exhibits resistance. In the bilayer resist method, a resist pattern is temporarily transferred to the lower film, and then the substrate for processing is etched by using the pattern-transferred lower film as an etching mask. In a representative example of the method, a silicon-containing resin is used for the photoresist film, and an aromatic resin is used for the lower film. In this method, a resist pattern is formed on a photoresist film including a silicon-containing resin. Then conducting oxygen reactive ion etching turns the silicon-containing resin into silicon oxide which has high etching resistance against oxygen plasma, and removes portions of the aromatic resin that is not covered by the silicon oxide serving as an etching mask, whereby the resist pattern on the silicon-containing resin is transferred to the lower film including the aromatic resin. Because optical transparency is not required at all as distinct from monolayer resist films, various resins with high etching resistance against etching with fluoride gas plasma or chloride gas plasma can be used as the aromatic resin. Then a substrate is etched with fluoride gas plasma or chloride gas plasma by using the lower film including the aromatic resin as an etching mask.
Besides the bilayer resist method, a trilayer resist method that can be conducted by using general photoresist film compositions used for the monolayer resist method is also known. In the trilayer resist method, in general, an organic film, a silicon-containing intermediate film thereon, and a photoresist film on the intermediate film are formed. The organic film includes an aromatic resin that is used as a lower film in the bilayer resist method and that has sufficiently higher etching resistance than a substrate.
In order to pattern the trilayer, firstly, a resist pattern is formed on the photoresist film by lithography. Secondly, the silicon-containing intermediate film is patterned with fluoride gas plasma by using the photoresist film as an etching mask. Use of fluoride gas plasma allows for large etching selection ratio between the photoresist film and the silicon-containing intermediate film. Thirdly, oxygen reactive ion etching is conducted to thus-obtained pattern, whereby the organic film including an aromatic resin on the substrate is etched by using the patterned silicon-containing intermediate film as an etching mask. In this way, in the trilayer resist method, combining etching conditions enables forming an etching mask pattern over a substrate that has sufficiently high etching resistance when the substrate is processed.
The silicon-containing intermediate film used for the trilayer resist method is broadly divided into organic silicon-containing films made of organic silicon-containing film compositions such as SOG films or antireflection silicone resin films; and inorganic silicon-containing films formed by the plasma CVD method etc. such as silicon oxide films, silicon nitride films, or silicon oxide nitride films.
As for the inorganic silicon-containing films, use of the high density plasma CVD method provides dense inorganic silicon-containing films. It is recognized that such films show excellent ion impact resistance, do not cause film loss or contraction, and provide organic film patterns faithful to design rules when an organic film which serves as an underlying layer of an intermediate film is subjected to dry etching (See Japanese Unexamined Patent Application Publication No. H07-183194). However, this case requires introduction of an expensive CVD apparatus and a wide area for installing the apparatus. Therefore, the case costs much and which is a problem.
Then organic silicon-containing films become a focus of attention because the films can be formed by spin-coating method etc. and do not require any extra apparatus such as a CVD apparatus. Among the organic films, antireflection silicone resin films particularly receive attention and have been developed because the antireflection films has a function to reduce reflection optically and have excellent preservation stability (See Japanese Unexamined Patent Application Publication No. 2005-15779).
In order to form a pattern with higher precision on a substrate, the following intermediate films are required: films that can maintain excellently resist pattern profile formed on an overlying photoresist film, that is, that show excellent resist compatibility; and that also show high etching resistance at the time of etching an underlying organic film. Up to now, there is no antireflection silicone resin film that has both excellent resist compatibility and high etching resistance at the time of etching an organic film. And the development of such a film has been awaited.